Another autumn arrives in New York with all the majesty and rich palette of changing colors and leaf fall and with it another fall migration. Bird watchers (and writers) entranced by the seasonal avian journey find skies full of winged travelers for glorious study. Birds flying south for warmer climates let us know that at least someone gets to get away for the winter, or so we think. For the birds, navigating through this city means that some make it and some will not make it out of here alive.
For all of wildlife, the number one human related threat is habitat loss or destruction. For birds, the second greatest danger is “window kills” or colliding with window panes. As biologist, Daniel Klem, Jr. notes: “birds behave as if clear and reflective panes are invisible to them, and they kill or injure themselves attempting to reach habitat seen through or reflected in windows.” Actual figures of birds killed every year in the US as a result of these collisions are unknown but Klem estimates them at 100 million to 1 billion with the modest assumption “that one bird is killed per building per year.” When it comes to dangers to birds, window-kills are not well publicized and are often overlooked despite their staggering numbers. Klem compares figures of other sources of “human associated” bird deaths: “120 million from hunting, 60 million from vehicle road kills, 10,000 to 40,000 from wind turbine strikes” per year, concluding that “The kills at clear and reflective glass and plastic are surely in the billions worldwide.” These sobering numbers highlight a need to raise awareness of a monumental conservation crisis for our birds and to adequately address it.
How birds see, what, when and where they are seeing contribute to the danger. A NYC Audubon study done in 2009 collected data on 5,400 bird collisions in Manhattan over a ten year period. Focusing on factors associated with window collisions, the study found that most victims (two thirds of the collisions resulted in fatalities) were migrating birds from the warbler, thrush and sparrow families. Bird strikes were also found to occur more frequently along “portions of the exterior glass surface that reflect outside vegetation.” The study further found that collisions were more like to happen during daylight hours as opposed to evening. The Audubon study concluded that that migrating birds are more at risk of window kills while Klem notes that the more birds around glass the more collisions, with our own misplaced bird feeders being just as likely, if not more so, to place birds at peril. Both statements are no doubt correct as long as glass is present for birds to fly into. (Keep reading)
Frania Shelley-Grielen is an animal behaviorist, contact her at http://www.animalbehaviorist.us